1. Field of the Invention
The present invention relates to a light source unit including a luminescent material plate tight covering and sealing construction in which a luminescent material plate is covered and sealed tight from the circumference thereof.
2. Description of the Related Art
In these days, data projectors are used on many occasions as an image projection apparatus which projects images including an image of a screen and a video image of a personal computer, as well as images based on image data which is stored on a card such as a memory card on to a screen.
In these data projectors, light emitted from a light source is caused to converge at a micromirror display element called a DMD (Digital Micromirror Device) or a liquid crystal panel so that a color image is displayed on a screen.
In addition, the application of such projectors is expanding widely from commercial presentation to domestic use as personal computers and DVD players have been used generally and have been spread widely in the market.
Conventionally, the mainstream of these projectors has been those which utilize a high-intensity discharge lamp as a light source. In recent years, however, there have been made many developments and proposals on projectors which use, as a light source, a semiconductor light emitting element such as a laser diode.
For example, Japanese Unexamined Patent Application (KOKAI) No. 2011-013316 discloses a light source unit which includes an excitation light source which employs a laser diode to emit light of a blue wavelength range and a luminescent wheel (a rotational plate) which has a layer of luminescent material which absorbs the light emitted from the excitation light source to convert it into visible light and which is driven to rotate by a motor, and a projector which includes this light source unit.
In addition, a plurality of luminescent materials are dispersed in a resin binder which is made of a transparent silicone or epoxy resin to form a luminous light emitting layer.
This resin binder is deteriorated by the excitation light from the semiconductor light source or is damaged particularly when the intensity of the excitation light is high.
Additionally, the resin such as the silicone or epoxy resin in which the luminescent materials are dispersed has a low thermal conductivity, and therefore, the temperature of the luminescent materials is increased, generating a phenomenon such as temperature extinction in which the wavelength of light emitted from the luminescent materials is shifted or the intensity of such light is lowered by the increase in temperature.
This calls for a reduction in the luminance of the light source unit.
Additionally, as a luminescent material which is relatively strong against heat, there is known a luminescent material employing a sintered ceramic as described in Japanese Unexamined Patent Publication (KOKAI) No. 2006-282447 (JP-A-2006-282447).
In a projector which employs the luminescent wheel described above, it is difficult to make its light source unit small in size. However, with the ceramic luminescent material, depending upon configurations, the luminescent material does not have to be driven to rotate, which facilitates the reduction in size of a luminous light emitting device and a projector employing the same.
However, even with the luminescent material described in JP-A-2006-282447, when dust sticks to the luminescent material, the temperature of the luminescent material is increased to thereby carbonize the dust sticking to the luminescent material, leading to fears that the luminescent material is destroyed or the luminance of luminous light emitted therefrom is lowered.